The overall goals of the proposal are to characterize the determinants of the response dynamics of the horizontal semicircular canal and to study the mechanisms and sequels of the efferent vestibular systems manipulation of these determinants. The response dynamics of the horizontal semicircular canal nerve have been documented in this species. There are three broad classes of afferent based upon their response dynamics across the frequency and amplitude spectrum studied. There are frequency and amplitude dependent non-linearities represented within the responses of certain classes of afferent. The contributions and significance of the putative differential motion of the center and periphery of the cupula and of hair cell receptor current frequency and amplitude dependent non-linearities to those in the primary afferents will be evaluated. Whole cell patch clamp techniques will be applied to hair cells isolated from defined functional regions of the crista to study the magnitude and kinetics of activation, inactivation, and deactivation of potassium currents. The current clamp responses to perturbing currents of these cells will be determined. Differential efferent action upon the various classes of primary afferent has also been documented. The implications and mechanisms of this differential action will be studied with morphological and physiological techniques. The amplitudes and shapes of miniature (m) EPSPs recorded from primary afferents will be measured before and during stimulation of efferents to assess the significance of the efferent evoked changes in EPSP characteristics to the output of the system. The activation sequelae of the efferent vestibular system upon horizontal canal afferents in free swimming fish will be studied utilizing multi-channel electrodes, under water acoustic telemetry and under water video. Thus, we hope to arrive at a general theory of efferent action in this species. Studies of the cellular and systems science aspects of the vestibular system and its efferent control add information about function and may bear upon possible future therapies and mechanisms for the control of motion sickness.